I am speaking in the moment of the facts on the ground and you are speaking of some grand invasion that is about as likely as a Detroit Lions Super Bowl win. We are much, much closer to nuclear war than we are to Putin's army marching on Warsaw.
Right now he is the bully who got his ass kicked. Great. High fives all around. That all changes when the little pussy goes home and gets his AK out of the closet, returns to the scene, and opens fire.
Just as guns are a great equalizer, so are nukes. I mean, if he really wanted to push this to the limit, and he does invade NATO, we would be obligated to respond in kind. There is no way he wins that war aside from the Charlie Sheen "winning" of planetary nuclear winter. He is gambling that he can make a Belarussia out of Ukraine and we won't go to the mat for that. And we shouldn't. And we can all step back from the brink and one day perhaps a chisel out a truly neutral Ukraine. Fuck, American Indians were able to do this shit. I remember reading that the longest word in the history of languages was some Massachusetts Indigenous word designating a lake that divided two warring tribes. The name meant "you fish on your side, we fish on our side, nobody fishes in the middle."
Although in Ukraine's case, I'd advise letting everybody fish in the middle. Make it the entrepot between east and west for trade and banking. Make it too valuable for either side to want to flatten. Just disarm it as near as possible and let the money flow.